Skip to main content

Problem 108: If the probability density of a random variable is given by; find the value k and the probability that the random variable takes on a value

Problem 108: If the probability density of a random variable is given by
$f(x)= \begin{array}{cc} \Bigg\{ & \begin{array}{cc} kx^3 & 0\le x\le1 \\ 0 & elsewhere \end{array} \end{array} $
find the value k and the probability that the random variable takes on a value
a. betweeen $\frac{1}{4}$ and $\frac{3}{4}$; b. greater than $\frac{2}{3}.$
Solution:
To find k, we must integrate $f(x)$ from $x=0$ to $x=1$ and set it equal to 1. Thus
$\int _{0}^{1}f(x)dx=1\Rightarrow \int _{0}^{1}k{x}^{3}dx=1\Rightarrow k\frac{{x}^{4}}{4}\Big|_0^1 =1 \Rightarrow k/4=1 \Rightarrow k =4$
a. betweeen $\frac{1}{4}$ and $\frac{3}{4}$;
$P(0.25\le X \le 0.75) = \int _{0.25}^{0.75}4{x}^{3}dx = x^4\Big|_{0.25}^{0.75} = 0.75^4-0.25^4 = 0.3125$

b. greater than $\frac{2}{3}.$ $P(X > \frac{2}{3}) = \int _{\frac{2}{3}}^{\1}4{x}^{3}dx = x^4\Big|_{\frac{2}{3}}^{1} =1^4 - \frac{2}{3}^4 = 0.802469$

Labels:

Comments

Post a Comment

Popular posts from this blog

Problem 98: If 6 of 18 new buildings in a city violate the building code, what is the probability that a building inspector, who randomly selects 4 of the new buildings for inspection, will catch
a. none of the buildings that violate the building code?
b. 1 of the new buildings that violate the building code?
c. 2 of the new buildings that violate the building code?
d. at least 3 of the new buildings that violate the building code?

Problem 98: If 6 of 18 new buildings in a city violate the building code, what is the probability that a building inspector, who randomly selects 4 of the new buildings for inspection, will catch a. none of the buildings that violate the building code? b. 1 of the new buildings that violate the building code? c. 2 of the new buildings that violate the building code? d. at least 3 of the new buildings that violate the building code? Solution: a. none of the buildings that violate the building code? Given that $x=0,n=4,a=6, N=18$ Hypergeometric distribution, $h(x;n,a,N)=\frac{\left(\begin{array}{c}a\\ x\end{array}\right)\left(\begin{array}{c}N-a\\ n-x\end{array}\right)}{\left(\begin{array}{c}N\\ n\end{array}\right)}$ $P(x=0) = h(0;4,6,18)=\frac{\left(\begin{array}{c}6\\ 0\end{array}\right)\left(\begin{array}{c}18-6\\ 4-0\end{array}\right)}{\left(\begin{array}{c}18\\ 4\end{array}\right)} = 0.16176.$ b. 1 of the new buildings that violate the building code? Given ...
Post a Comment
Read more

Problem 105: If a bank receives on the average α = 6 bad checks per day, what are the probabilities that it will receive (a) 4 bad checks on any given day?
(b) 10 bad checks over any 2 consecutive days?

Problem 105: If a bank receives on the average α = 6 bad checks per day, what are the probabilities that it will receive (a) 4 bad checks on any given day? (b) 10 bad checks over any 2 consecutive days? Solution: Poisson distribution, $f(x;\lambda )=\frac{{\lambda }^{x}{e}^{-\lambda }}{x!}$ a. 4 bad checks on any given day Given that $x=4, \lambda = \alphaT = 6\dot 1 = 6$ $f(4;6 )=\frac{{6 }^{4}{e}^{-6 }}{4!} = 0.134$ b. 10 bad checks over any 2 consecutive days Given that $x=10, \lambda = \alphaT = 6\dot 2 = 12$ $f(10;12 )=\frac{{12 }^{10}{e}^{-12 }}{10!} = 0.104837$
Post a Comment
Read more

Problem 57: Determine whether it is a subspace of the given vector space $\V$
$\V = \R^2$, and $S$ is the set of all vectors $(x, y)$ in $\V$ satisfying $3x + 2y = 0$.

Problem 57: Determine whether it is a subspace of the given vector space $\V$ $\V = \R^2$, and $S$ is the set of all vectors $(x, y)$ in $\V$ satisfying $3x + 2y = 0$. Solution: $S = \{x \in \R^2 : 3x+2y=0\}$. Let $(x_1,x_2),(y_1,y_2) \in S$. Then $3x_1+2x_2 = 0$ and $3y_1+2y_2 = 0$ Hence, $x + y = (x_1,x_2)+(y_1,y_2) =3x_1+2x_2 + 3y_1+2y_2 = 3(x_1+y_1) + 2(x_2+y_2)$ which implies that $(x_1+y_1,x_2+y_2) \in S$ Consequently, $S$ is closed under addition. Let $a \in \R$ and $(x_1,x_2) \in S$, then $ax = a(x_1,x_2) = a(3x_1+2x_2) = a0 = 0$ $=3(ax_1) + 2(ax_2) =0 $, which implies that $(ax_1,ax_2) \in S$ Therefore $S$ is also closed under scalar multiplication. It follows that $S$ is a subspace of $\R^2$.
Post a Comment
Read more